2021, January 21: Morning Stars, Evening Bright Moon

January 21, 2021:  Several bright stars are in the morning sky.  This morning look for Antares in the east-southeast.  Mercury – near its greatest elongation – is in the west-southwest after sunset.  Mars and the moon are near each other.  Planet Uranus is near Mars.

by Jeffrey L. Hunt

Chicago, Illinois:  Sunrise, 7:12 a.m. CST; Sunset, 4:52 p.m. CST.  (Note that sunset is approaching 5 p.m. CST) Check local sources for sunrise and sunset times for your location.

The morning sky is without any bright planets, Venus is nearing its superior conjunction with the sun, although that is two months away.

Venus has been visible as a morning star since early June.  You might still find it very low, less than 3° in altitude, above the east-southeast horizon about 30 minutes before sunrise.

This morning the bright star Antares – the Rival of Mars – is low in the south-southeast.  The star is emerging from its solar conjunction into the morning sky. 

The star is part of the constellation Scorpius the Scorpion.  The chart above shows the star’s place in the sky about one hour before sunrise.  Two other stars – Zubenelgenubi and Zubeneschamali – could be the pincers of the celestial critter.  Now they are part of Libra.

As the image above shows, Mars was near Antares a year ago.  Antares is about the same color as the planet and mostly about the same brightness.

Antares is a very large star, known as a supergiant star.  According to astronomical models, the star is near the end of its stellar life.  When the combination of hydrogen atoms in a star’s core ends, the center of the star contracts to raise temperatures to fuse heavier atomic nuclei.  In response the outside layers of the star expand and cool.  These stars are so large that if they were our sun, many of the planets would be inside it.

This bright star shines from about 500 light years away.  It can be seen at this great distance because it has the brightness of nearly 3,000 suns.

Evening Sky

Mercury is visible in the evening sky about 30 minutes after sunset.  It is low in the west-southwest.  Use a binocular to locate it in the bright twilight.

In two evenings, it is at its greatest angular separation from the sky, only 18.6°.  The planet does not appear very high in the sky when it is farthest from the sun.

The moon is farther eastward and as the sky darkens further, Mars is visible to the upper right of the bright gibbous moon.

Just one day after its conjunction with Uranus, Mars is still nearby.  Planet Uranus is barely visible to the unaided eye under ideal conditions.  With the bright moon in the sky, a binocular is needed to locate the starfield and the distant planet.

The dim star 19 Arietis (19 Ari on the chart) is 1.0° from Mars.  Uranus is nearly double that distance (1.7°) to the lower right of Mars.  The planet is distinctly aquamarine in color and appears as a “star” through a binocular.  A telescope with at least 100x magnification is needed to see the planet as an ultra-miniature world.

Mars continues to parade eastward through Aries.  The constellation’s brightest stars are far away from the ecliptic, where the sun, moon, and planets seem to move.  Mars is 8.8° below Hamal, the group’s brightest star.

Read about Mars during January.

Detailed Note: One hour before sunrise. Antares (α Sco, m = 1.0) is nearly 16° in altitude above the south-southeast horizon. The moon is at apogee (251,232 miles) at 7:11 a.m. CST.  Thirty minutes after sunset, Mercury is 8.0° up in the west-southwest.  The gibbous moon (8.8d, 61%) is farther east to the lower left of Mars.  As the sky darkens further, Mars is over two-thirds of the way up in the south.  It is 8.8° below Hamal, 1.0° to the lower left of 19 Ari, and 1.7° to the upper left of Uranus.

Read more about the planets during January.